Exercises 131 The Falling Apple (page 233) 1 Describe the legend of Newton s discovery that gravity extends throughout the universe According to legend, Newton saw an apple fall from a tree and realized that the moon falls toward Earth for the same reason an apple falls from a tree They are both pulled by Earth s gravity 2 Newton understood the concept of inertia, developed by Galileo, that without an outside force, moving objects continue to move at constant speed in a straight line 3 Is the following sentence or? Circular motion is accelerated motion, which requires a force 132 The Falling Moon (pages 233 235) 4 Newton realized that the moon must be falling Earth around 5 Is the following sentence or? The moon falls beneath the straight line it would follow if no force acted on it 6 Newton compared motion of the moon to a cannonball fired from the top of a high mountain Describe the possible paths for the cannonball proposed by Newton A cannonball fired with a small horizontal speed would follow a parabolic path and soon hit Earth If the speed were faster, the path would be less curved and the cannonball would hit Earth farther away At a fast enough speed, the path would become a circle and the cannonball would circle indefinitely 7 Circle the letter of the word that best describes the tangential velocity that prevents the moon from hitting Earth a upward b sideways c downward d backward 8 Is the following sentence or? Newton believed that the mass of the moon affects how it falls 9 Explain Newton s calculation that the moon falls 14 millimeters each second An apple falls about 5 m in its first second of fall The moon is about 60 times farther from the center of Earth than an apple at Earth s surface The moon should fall 1/(60) 2 of 5 m, or 14 millimeters in one second Conceptual Physics Reading and Study Workbook 103
133 The Falling Earth (page 236) 10 Is this sentence or? Newton s theory of gravity confirmed the Copernican theory of the solar system 11 Circle the letter of the sentence that describes the motion of a planet if its tangential velocity were reduced to zero a It would drift in space b It would continue in orbit at a slower speed c It would crash into the sun d It would spin away from the solar system 12 Why are there no large objects in the solar system today with very low tangential velocities? They long ago crashed into the sun 134 Newton s Law of (pages 237 239) 13 Is the following sentence or? Isaac Newton discovered gravity 14 State Newton s law of universal gravitation using words For any pair of objects, each object attracts the other object with a force that is directly proportional to the product of the masses of the objects and inversely proportional to the square of the distance between their centers of mass 15 What is the equation for universal gravitation? F = G [m 1 m 2 /d 2 ] 16 The constant G in this equation is called the and describes the strength of gravity 17 The English physicist Henry Cavendish first measured G 18 Is the following sentence or? The force of gravity is the strongest of the presently known four fundamental forces 19 Is the following sentence or? At the top of a mountain, your weight is slightly less than at ground level 135 Gravity and Distance: The Inverse-Square Law (pages 240 241) 20 Express the inverse square law in words 21 Circle the letter of the inverse square of 9 a 1 b 1 3 81 c 3 d 81 universal gravitational constant If one quantity is multiplied by a factor, another quantity decreases by the square of that factor 104 Conceptual Physics Reading and Study Workbook
Match each change with the effect it would have on the force of gravity between two objects Change Effect c a 22 The mass of one object doubles 23 The mass of one object decreases by half a The force is divided by 2 b The force is divided by 4 c The force is multiplied by 2 b 24 The distance between the objects centers of mass doubles d The force is multiplied by 4 d 25 The distance between the objects centers of mass decreases by half 26 Is the following sentence or? The gravitational influence of every object is exerted through all space 136 Gravitational Field (pages 242 243) 27 The pulls that Earth and the moon exert on each other is action at a distance because the bodies interact without being in contact 28 Define gravitational field a force field that exists in the space around every massive body 29 Earth s gravitational field interacts with objects by causing them to experience gravitational forces 30 Field lines show the strength and direction of a force field 31 Field lines are closest together where a field is strongest 32 How are gravitational field lines related to the acceleration of an object around Earth? Any mass near Earth will be accelerated in the direction of the field lines at that location 137 Gravitational Field Inside a Planet (page 244) 33 Circle the letter that identifies the location where Earth s gravitational field is zero a in a plane above Earth s surface b at Earth s surface c between Earth s surface and its center d at Earth s center 34 Is the following sentence or? The weight of a rock at Earth s center is zero 138 Weight and Weightlessness (pages 245 246) 35 Why are people often unaware that gravity accelerates us? because we are almost always in contact with Earth weight 36 Pressure against Earth is the sensation we interpret as Conceptual Physics Reading and Study Workbook 105
Match each position or movement of an elevator with your weight if you stepped on a scale in the elevator b d c Elevator Position or Movement Weight Reading 37 sitting still a no weight 38 accelerating downward b normal weight 39 accelerating upward c greater weight than usual a 40 falling freely d less weight than usual 41 Rather than define your weight as the force of gravity that acts on you, it is more practical to define weight as the force you exert against a supporting floor 42 Is the following sentence or? Weightlessness is the absence of gravity 43 Explain why rotating giant wheels will likely be used as space habitats in the future Rotation will supply a support force for astronauts, giving them a sense of weight 139 Ocean Tides (pages 246 248) 44 How often does a high tide occur? twice per day 45 Is the following sentence or? The pull of the moon and Earth on each other causes them both to be slightly elongated rather than spherical 46 The figure shows the moon near the spinning Earth Use the figure to explain the cause of ocean tides on Earth In your explanation, describe why the arrows in the figure are different lengths The arrows show that the gravitational pull of the moon is stronger on the ocean water nearest the moon and weaker on the opposite side, causing a bulge on each side As Earth spins, a fixed point moves under both bulges each day 47 Circle the letter of the fraction that compares the sun s contribution to ocean tides to the moon s contribution a one sixteenth b one fourth c one eighth d one half 48 The sun s pull on Earth is 180 times greater than the moon s pull on Earth 106 Conceptual Physics Reading and Study Workbook
49 Write or neap on each line to indicate whether the description matches a tide or a neap tide neap a Occurs when the moon is halfway between a new moon and a full moon b High tides are higher than usual, and low tides are lower than usual c Occurs at times of a new or full moon neap d The pulls of the moon and sun are perpendicular to each other e Occurs when the sun, Earth, and moon are all lined up f The solar and lunar tides coincide neap g The solar and lunar tides do not overlap 50 A tidal effect causes the solid surface of Earth to rise and fall as much as one-quarter meter twice each day 51 Explain why lakes have almost no tides There is no significant difference in the moon s pull on different parts of the lake 1310 Black Holes (pages 249 251) 52 Explain the effects that the following processes have on stars like our sun a Gravitation: b Nuclear fusion: It blows solar material outward 53 If the fusion rate of the sun increases, the sun will get and bigger 54 If the fusion rate of the sun decreases, the sun will get and smaller It tends to crush all solar material toward the center hotter 55 Circle the letter that identifies the fuel for the type of fusion that currently takes place in the sun a carbon b hydrogen c nitrogen d oxygen 56 Explain what will cause our sun to collapse some 5 billion years from now The sun will run out of hydrogen fuel for fusion, and gravitation will dominate cooler 57 As the sun collapses, a different type of fusion will begin in which helium fuses into carbon 58 Fusion will eventually cause the sun to expand into a(n) red giant which will extend beyond Earth s orbit and swallow Earth 59 When our sun no longer gives off heat and light, it will be a(n) black dwarf Conceptual Physics Reading and Study Workbook 107
60 Explain why a star that is at least two to three times more massive than our sun will eventually collapse into a black hole It is so massive that its collapse will not stop and its density will become infinite 61 Circle the letters of the statements that correctly describe a black hole a It has significantly more mass than the star from which it collapsed b Its gravitational field beyond the original radius of the star is unchanged c The configuration of the gravitational field around it represents a collapse of space itself d Its volume is unchanged from the star from which it collapsed 62 Explain how a black hole that is part of a binary pair can be detected, even though it cannot be seen Matter streams from the visible star of the binary pair toward the black hole, emitting X-rays that can be detected by telescopes 63 Black holes are near the centers of most galaxies How do these black holes affect stars near them? They cause the stars to speed around in tight orbits 1311 (pages 251 254) 64 Refer to the figures above to describe the role that gravity played in the formation of the solar system A slightly rotating ball of interstellar gas contracted due to mutual gravitation To conserve angular momentum, the rotational speed of the gas increased, and the particles moved out, producing a disk shape The greater surface area caused the matter to cool and form clusters that became planets 108 Conceptual Physics Reading and Study Workbook
65 Explain why Earth is round 66 Define perturbation 67 Circle the letter of the orbiting body that was discovered in just half an hour because of a perturbation in the orbit of Uranus a Jupiter b Neptune c Pluto d Saturn Match each type of energy or matter with its percent of the universe Energy or Matter Percentage of the Universe c b Gravity caused Earth to attract itself together before it became solid Any corners of Earth have been pulled in so that Earth is a giant sphere the deviation of an orbiting object from its path around a center of force, caused by the action of an additional center of force 68 dark energy a 4% 69 dark matter b 23% a 70 ordinary matter c 73% 71 Is the following sentence or? The law of universal gravitation is a complicated law that only describes a few unique instances Conceptual Physics Reading and Study Workbook 109